Configuration variables on the MarkdownExtra parser work the same way.

Markdown Configuration

empty_element_suffix = " />"

This is the string used to close tags for HTML elements with no content
such as <br> and <hr>. The default value creates XML-style empty
element tags which are also valid in HTML 5.

tab_width = 4

This is the width of a tab character on input. Changing this will affect
how many spaces a tab character represents.

Note: Keep in mind that when the Markdown syntax spec says “four spaces
or one tab”, it actually means “four spaces after tabs are expanded to
spaces”. So setting tab_width to 8 will make the parser treat a tab
character as two levels of indentation.

hard_wrap = false

Setting this to true will change line breaks into <br /> when the
context allows it. When set to false, following the standard Markdown
syntax these newlines are ignored unless they a preceded by two spaces.

no_markup = false

Setting this variable to true will prevent HTML tags in the input from
being passed to the output.

Important: This is not a protection against malicious javascript
being injected in a document. See why in Markdown and XSS.

no_entities = false

Setting this variable to true will prevent HTML entities (such as &lt;)
from being passed verbatim in the output as it is the standard with
Markdown. Instead, the HTML output will be &amp;tl; and once shown in
shown the browser it will match perfectly what was written.

predef_urls = array()

You can predefine reference links by setting predef_urls to a list of
urls where the key is the name of the reference. For instance:

$parser->predef_urls = array('ref' => 'https://michelf.ca/');

will make this Markdown input to create a link:

This is [my website][ref].

predef_titles = array()

Use predef_titles to set the title of the link references passed in
predef_urls. As for predef_urls, the key is the reference name.

url_filter_func = null

This variable makes it possible to transform URLs for links and images
in the document by specifying a function:

$parser->url_filter_func = function ($url) {
return tolower($url);
};

This can be used to fix unsecure URLs, transform local URLs into
complete ones, etc.

header_id_func = null

Headers can have their id attribute auto-generated by setting this
configuration variable to a function:

A more advanced version could infer the language of the code and perform
syntax coloring. The result returned by this function is automatically
wrapped in a <code>.

enhanced_ordered_list = false

Setting this to true allows ordered list to start with a number
different from 1.

(Note: this is set to true by default for Markdown Extra.)

Markdown Extra Configuration

In addition to all the configuration variables in the Markdown parser, the
MarkdownExtra parser has the following extra settings.

fn_id_prefix = ""

A prefix for the id attributes generated by footnotes. This is useful
if you have multiple Markdown documents displayed inside one HTML document
to avoid footnote ids to clash each other.

fn_link_title = ""

fn_backlink_title = ""

An optional title attribute for footnotes links and backlinks. Browsers
usually show this as a tooltip when the mouse is over the link.

For backlinks, the title is also used as an accessibility label with the
aria-label attribute.

fn_link_class = "footnote-ref"

fn_backlink_class = "footnote-backref"

The class attribute to use for footnotes links and backlinks.

fn_backlink_html = "&#8617;&#xFE0E;"

HTML content for a footnote backlink. The &#xFE0E; suffix in the default
value is there to avoid the curled arrow being rendered as an emoji on
mobile devices, but it might cause an unrecognized character to appear
on older browsers.

code_class_prefix = ""

An optional prefix for the class names associated with fenced code blocks.
This will be prepended to the class name if you write your fenced code block
this way:

~~~~ .html
<br>
~~~~

Note however that it has no effect if you add a class name using the more
generic extra syntax that uses braces:

~~~~ {.html .flashy}
<br>
~~~~

code_attr_on_pre = false

When set to false (the default), attributes for code blocks will go on the
<code> tag; setting this to true will put attributes on the <pre> tag
instead.

table_align_class_tmpl = ""

Value for the class attribute determining the alignment of table cells.
The default value, which is empty, will cause the align attribute to be
used instead of class to specify the alignment.

If not empty, the align attribute will not appear. Instead, the value for
the class attribute will be determined by replacing any occurance of %%
within the string by left, center, or right. For instance, if the
configuration variable is "go-%%" and the cell is right-aligned, the result will
be: class="go-right".

predef_abbr = array()

You can predefine abbreviations by setting predef_abbr to a list of
abbreviations where the key is the text of the abbreviation and the value
is the expanded name.

hashtag_protection = false

When set to true, prevents ATX-style headers with no space after the initial
hash from being interpreted as headers. This way your precious hashtags
are preserved.

Differences with classic version

Configuration options for the classic version are mostly the same as those
of PHP Markdown Lib described above. Still, here are some notable differences:

For the classic version, classes are named Markdown_Parser and
MarkdownExtra_Parser, with no namespace.

The defaultTransform function does not exist. Instead a global Markdown
function is available and uses either Markdown_Parser or
MarkdownExtra_Parser depending on which file you download. The parser class
used by the Markdown function can changed by defining the
MARKDOWN_PARSER_CLASS constant prior including the file.

Default options are defined in similar constants, which can also be defined
prior including the file to set the defaults.

In the classic version, a rel="footnote" attribute is added on links to
footnotes, and a rev="footnote" on the backlinks. In the default configuration
there is no class attribute. The Lib version replaces rel and rev with the
class attribute defined earlier in this document.